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LM48511 - output locked low

Luca Trianni
Prodigy 30 points
Other Parts Discussed in Thread: LM48511

Hi.

I've designed a board using an LM48511 as speaker amplifier. Sometimes, if input signal is high enough or I try increasing amplifier gain "too much", output to speaker gets to 0. Moreover, output remains low until power supply board is switched off-on. The output stage seems to get locked low and being freezed in that state.

I've found a previous post (e2e.ti.com/.../193746 ) talking of a similar problem, and explaining everything with an undervoltage on power supply VDD (below 3V). I've checked 5V VDD and it actually goes below 3V when output lock happens. I've disabled boost converter (using 5V VDD to directly supply internal opamp and output stage), but output lock still happens, eventhough less often.

What I don't understand is why output remains low even after VDD returns to nominal value 5V. Could reset signals be used to make amplifier still working without resetting power supply?

Thanks...

  • 0
    TI__Mastermind 20085 points
    Hi Luca

    Welcome to E2E, thank you for your interest in our products.
    I think that this condition happens because the quiescent current of the boost regulator is related to the difference between its input and output voltages, the larger the difference, the higher the quiescent current. It is possible that the input's value is changed until that the quiescent current is too much high, then the device actives short circuit protection. The device's output gets locked low when the device actives the protection.
    Regarding how to reset the device, Have you tried to reset the device used the shutdown pin?

    Best Regards
    Jose Luis Figueroa
    Audio Applications Engineer | A-Team
  • 0 in reply to José Luis
    Prodigy 30 points

    Thanks for your answer. Just to understand, does this quescient current check happen even when boost regulator is not enabled?Actually I've measured power supply on pin 18 and 13 and, while VDD (pin18) has a glitch to 1.25V, while power on pin 13 remains at about 4,5V (due to inductance-output capacitor effect). So there's a short time difference in input-output boost, but I'm working without boost.

    Anyway I'm managing my 5V voltage regulator to avoid deep undervoltage on supply.

    As you suggested, a cycle on SD_AMP signal can "wake up" the output stage and makes amplifier still working.

    Regards 

  • 0 in reply to Luca Trianni
    TI__Mastermind 20085 points
    Hi Luca

    Maybe a design error could be caused this condition. When you manage the 5V voltage regulator, doesn't this condition happen?

    Best Regards
    Jose Luis Figueroa
    Audio Applications Engineer | A-Team
  • 0 in reply to José Luis
    Prodigy 30 points

    Hi Jose, thanks for your reply.

    I've managed power supply to avoid undervoltage on VDD (increased output capacitor, changed DC-DC converter...).
    I've come to a point where power supply voltage is stable, but making tests with a load less than 4 ohm I still get the amplifier blocked. Can you tell me which value of output current makes the amplifier to freeze low its output? Moreover, what's the maximum output power into a 4 ohm speaker I can obtain with VDD=5V and boost regulator disabled?

    Thnks

    Luca

  • 0 in reply to Luca Trianni
    TI__Mastermind 20085 points
    Luca,

    This device is designed to work with a load higher or same than 4Ω. If you use a load lower than 4Ω, the power dissipation increases until that the device activates the protection.

    Best Regards
    Jose Luis Figueroa
    Audio Application Engineer | A-Team